Radio system using nodes

ABSTRACT

A radio communication route enables communication from an originating ground station to a destination ground station via one of multiple randomly orbiting, rotating satellites with no active attitude control. The ground stations and satellites include directional antennas for receiving radio signals from and transmitting radio signals in multiple directions. The satellites store an address of a destination ground station from which an initial information signal is transmitted and antenna information identifying the satellite antenna on which the initial information signal was received. Plural satellite antennas transmit linking information identifying the satellite to the originating ground station. Data transmissions received at the originating ground station that designate a particular destination are transmitted by the originating ground station using the antenna on which the linking information was received and the satellite retransmits the data transmission using the satellite antenna identified by the stored antenna information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional applications No.62/379,601, filed Aug. 25, 2016, and no. 62/396,181, filed Sep. 18,2016, the entire contents of both of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to radio mesh systems using satellites inrandom orbits in communication with ground stations includingground-based receivers and transmitters for cellular telephonecommunications and Internet connections, and more particularly, tosystems and methods of automatically establishing radio routes betweenground stations using one or more unguided or substantially unguidedsatellites deployed randomly or quasi-randomly in low-earth orbits.

Description of Related Art

A brief history of certain aspects of cellular telephony relevant to thepresent disclosure is set forth in U.S. Pat. No. 5,793,842, which namesas an inventor Jerry R. Schloemer, who is also the present inventor. Oneearly system architecture, still in use today, involved a limited numberof tower-mounted transceivers (“drops”) and plural mobile radios(“cellular telephones”). In these early systems, and still in some casestoday, a central computer controlled communications between land linesconnected to the towers and the mobile radios. Implementing this systemarchitecture required significant investment in infrastructure andcomputing power, especially as the increasing popularity and technicalcapabilities of cellular telephones necessitated increased systemcapacity and sophistication. An alternate system architecture involvedusing radio transceivers (“nodes”) mounted on existing structures, suchas buildings and telephone poles. These architectures use nodes capableof receiving and transmitting signals to and from cellular telephonesalong a radio route among the nodes to drops at selected nodes. Thiscame to be called a mesh network, an early example being the systemdisclosed in Cox, Donald C., “Wireless Network Access for PersonalCommunications,” IEEE Communications Magazine (December 1992), pp96-115.

A particular challenge in implementing mesh systems was how to determinethe best available radio routes for interconnecting the nodes.Generally, early mesh systems still required a central computer to makerouting determinations, which added to system complexity and cost. Otherapproaches, such as that described in U.S. Pat. No. 4,937,822 to Weddleet al., involved a mesh system in which routes would be establishedautomatically, that is, without a central computer. However, Weddledisclosed such a system only in a mesh in which the nodes are laid outin a regular rectangular grid and radio routing links can only bebetween nodes orthogonally adjacent to each other (that is, cater-cornerlinks between nodes would not be permitted). The shortcomings of such asystem will be immediately apparent to those skilled in the art, if forno other reason than in a real-world setting it would be very difficult,if not impossible, to distribute nodes in a strictly orthogonal,uniformly-spaced rectangular grid over a wide enough area to make thesystem practicable. Moreover, Weddle does not disclose in detail anyalgorithm by which the nodes would actually create a preferred radioroute.

Against that background the present inventor's U.S. Pat. No. 5,793,842disclosed a system and method of creating radio routes through a mesh ofnodes that were not limited in their placement and did not require acentral computer. The systems and methods described in detail furtherbelow in connection with the present invention take advantage oftechnology described in U.S. Pat. No. 5,793,842 relating to the creationof radio routes through plural, randomly located nodes and thetransmission of communications using those routes. To avoid thenecessity of setting forth here the details of these types of systemsand methods, the disclosure in U.S. Pat. No. 5,793,842 relating to routecreation, and digital and analog signal transmission using the routesthus created, is incorporated herein by reference as if set out in full.

The inventor improved on that technology in his later U.S. Pat. No.6,459,899, which, among other things, describes a system that uses nodeswith directional antennas to improve the route creation andcommunication transmission capabilities of the earlier system. Thisimprovement solves complex issues presented by using nodes withdirectional antennas in the systems and methods described in the '842patent, and thus takes advantage of the higher quality radio linksachievable with directional antennas. The present invention also usesthe technology disclosed in the '899 patent, and its descriptions ofroute creation are incorporated by reference herein.

Before the inventor's approach to creating routes through a radio meshnetwork with randomly distributed nodes and no central computer, otherswere proposing ways to provide worldwide cellular coverage usingsatellites for call transmission between earth-based originating anddestination drops. An example of a satellite system that was actuallycommercialized is disclosed in various patents such as U.S. Pat. No.5,274,840 to Schwendeman and U.S. Pat. No. 5,410,728 to Bertiger et al.,both of which are assigned to Motorola, Inc. This system utilizedsatellites evenly distributed in a predetermined number of polar orbitsas transceivers for signals between satellites and between satellitesand transceivers on the ground. A sufficient number of satellites isused to provide coverage of the entire globe. However, in practice thissystem, which was commercialized by Iridium, had numerous drawbacks. Onewas that each satellite needed onboard thrusters, rocket fuel, andnavigational hardware to maintain its desired orbit. This increasedsatellite size and weight, which increased the launch cost, as well asincreasing the cost of the satellite itself. Also, to account forinevitable satellite failures, extra satellites would have to bemaneuvered into a failed satellite's orbit, thus increasing the cost ofthe entire system by requiring extra satellites and their concomitanthigh manufacturing and launch costs. See, for example, “IridiumSatellite Constellation,” Wikipedia,https://en.wikipedia.org/wiki/Iridium (last visited May 9, 2017).Ground-based orbit and attitude control using complex computertechnology further increased system costs. In the end, its drawbacksmade the system commercially unviable for mass market applications,although it is believed to have found use in specialized areas such asmilitary applications and reporting by journalists from remote areas.

In addition to maintaining each Iridium satellite in a particularorbital position relative to the earth and other satellites, theattitude of each satellite also had to be maintained within certaintolerances so that its antennas would be oriented for effectivesatellite-satellite and satellite-ground radio communications. One wayof providing attitude control was using onboard thrusters, which presentthe drawbacks already discussed. Various mechanically-based inertialattitude control systems have been proposed, such as those described inU.S. Pat Nos. 3,017,777 and 8,164,294, and in Chabot, J. A., “ASpherical Magnetic Dipole Actuator for Spacecraft Attitude Control,”Thesis for M.S. in Aerospace Engrg. Sciences, Univ. of Colorado, 2015.However, it is believed that these types of systems would not performany better than rocket-based attitude control, while their mechanicalcomplexity and onboard control systems would preclude significantsavings in weight as compared to rocket-based attitude control.

The present inventor disclosed in his U.S. Pat. No. 5,566,354 asatellite cellular telephone system that improved on theMotorola-Iridium approach. The inventor's improved approach allowed thesatellites to occupy random orbits. This eliminated the orbital controlcomponents of satellite systems that relied on each satellite being in aknown location relative to the others, such as the Motorola-Iridiumsystem or the wireless telephone/satellite system disclosed in U.S. Pat.No. 5,303,286. However, the random-orbit system described in the '354patent has certain drawbacks, one of which is that the satellites stillrequire attitude control to insure that the satellite antennas point inthe correct directions. Nor, as discussed in detail further below, doesit have the advantages of a true mesh system, as that term is used inthis description.

Aside from the rapid spread of cellular telephone usage around the worldin recent years, access to the Internet through computers andsmartphones has become a necessity for businesses and individuals alike.It is difficult to do business or manage personal affairs effectivelywithout access to Internet-based resources like email, electronicbanking, investigative/search services, and many others. In addition,social media providers like Facebook and Twitter can only exist in areasof the world that provide Internet access. A satellite-based systempresents an ideal way of making the Internet and cellular telephoneservice available in remote areas without blanketing a country withtowers or installing land-based radio mesh nodes across vast areas.However, known satellite systems suffer from numerous drawbacks, some ofwhich are discussed above, and none has been successfully commercializedto date. In fact, a low-cost satellite system would have the potentialto replace tower-based systems and ground-based mesh systems altogether.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a radiocommunication system comprising a plurality of satellites capable ofestablishing radio links between orbiting satellites and between thesatellites and ground-based stations without requiring the satellites tobe maintained in predetermined orbits or in predetermined attitudesrelative to each other or the earth. In a preferred embodiment there area sufficient number of satellites to provide a satellite mesh thatensures almost to a certainty that any spot on the earth's surface willbe within sight of at least one satellite at all times. One specificembodiment utilizes at least 200 satellites.

One aspect of the invention rests in part on incorporating in each suchsatellite a plurality of antennas capable of transmitting and receivingin all directions. A radio link can be created when a radio beamtransmitted from an antenna in one satellite is received by an antennain another satellite. This is sometimes referred to herein as a “beammatch.” The inventor recognized that using a unique antenna arrangementand uniquely coded radio transmissions from the satellites and groundstations, and treating both as nodes in a mesh, would enable a radioroute to be established between ground stations by assembling radiolinks via one or more of the satellites. One insight that led to thisaspect of the invention is that the satellites' attitudes and relativepositions change sufficiently slowly as compared to the time that ittakes the on-board computers in each satellite to calculate a radioroute. Accordingly, once the radio route is established, communications(“calls”) between the ground stations via one or more of the satellitesare not normally disrupted or, in the event that an existing route isdisrupted as a satellite moves or tumbles, a new radio route can beestablished “on the fly” with the same or different satellites while thecall is in progress. As used in the description that follows, a “call”is a communication of content (digital or otherwise) over a radio routebetween satellites or between a satellite and a ground station, unlessotherwise indicated explicitly or by context. While not limited as such,the systems described herein are particularly well suited for thetransmission of data in packets, defined here in the generally acceptedsense as a collection of digital data with a portion representing thecontent of the transmission (sometimes referred to as the “payload”),and a control portion (sometimes referred to as a “header” or“trailer”), which contains information enabling the payload to bedelivered successfully, such as source and destination addresses, errordetection codes, and sequencing information.

In one of its more general aspects the present invention uses a uniquesatellite construction with on-board computers that can performcalculations and select antennas to create radio routes between groundstations via one or more satellites virtually in real time as thesatellites move in uncontrolled orbits with no attitude control. Theradio routes are determined by algorithms executed by the computers inthe satellites, so that a central computer is not needed to specifywhich satellite or satellites will comprise an optimum radio routebetween ground stations.

One embodiment of the invention uses the disclosed satellite mesh tocreate an optimum radio route that comprises a single satellite thatprovides a radio route between two ground-based transceivers. The uniquesatellite design described herein enables a single-satellite route to bemaintained even as the satellite tumbles with no attitude control or ifconditions change so that another satellite in sight of the ground-basedtransceivers will provide a better radio route because the firstsatellite drifted out of range or became inoperative for some reason.

A particular advantage of the system disclosed herein is that in apreferred embodiment it provides the above features and those describedin more detail below by blanketing the earth with lightweight,battery-powered satellites that reduce launch costs and eliminate thenecessity for complex and costly control systems for maintaining thesatellites in particular orbits and in particular attitudes. Anotheraspect of the invention uses ground stations with an antenna arrangementdifferent from that used in the satellites, since the limitations onsatellite weight, size, and power do not apply to the ground stations.This means that the ground stations can have a greater antenna density(more antenna beams over a given spherical area) and use antennas withmore power (gain), thus virtually ensuring that data communications willbe possible between any two ground stations.

Another embodiment of the invention enhances the ability of thesatellites to establish radio links between satellites and between asatellite and a ground station by using satellites that spin or rotateabout an axis. This increases the probability of creating a beam matchbetween two satellites because each satellite is likely to “see” moreantennas on other satellites during a given period of time. This enablesthe use of higher-gain antennas with correspondingly narrower beamwidths, thus increasing the strength of the radio links and thereliability of call transmissions, Typically, the satellites aredeployed with a predetermined angular velocity, which may be differentfor different satellites. In one variation of this embodiment, thesystem includes satellites that rotate in opposite directions. Furtherconsiderations for realizing this embodiment are discussed in thedetailed description that follows.

These and other aspects and features of the invention and embodimentsthereof will be covered in more detail as this description proceeds.

This Summary is provided solely to introduce in a simplified form aselection of concepts that are described in detail further below. It isnot intended necessarily to identify key or essential features of thesubject claimed herein, nor is it intended to be used an aid indetermining the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects of the invention will be better understood from the detaileddescription of its preferred embodiments which follows below, when takenin conjunction with the accompanying drawings, in which like numeralsand letters refer to like features throughout. The following is a briefidentification of the drawing figures used in the accompanying detaileddescription.

FIG. 1, comprising FIGS. 1A and 1B, schematically depicts the radio meshconcept disclosed in the inventor's U.S. Pat. Nos. 5,793,842 and6,459,899.

FIG. 2, comprising FIGS. 2A and 2B, illustrates certain geometricprinciples underlying the space-based radio systems disclosed andclaimed herein.

FIG. 3 schematically depicts an embodiment of a satellite suitable foruse in the space-based radio systems disclosed and claimed herein.

FIG. 4 is a representation of various operational components of thesatellite depicted in FIG. 3.

FIG. 5 illustrates an embodiment of a process using a single satellitefor creating a radio route between two ground stations.

FIG. 6 illustrates how a satellite radio mesh system as described hereinusing a single satellite can be used to provide radio routes within aprescribed geographical area such as the country of Egypt.

FIG. 7 illustrates the relation between the distance separating twopoints on the earth's surface and the overlapping area of twointersecting circles centered on the respective points.

FIG. 8, comprising FIGS. 8A, 8B, and 8C, schematically depicts rotatingsatellites in accordance with an alternate embodiment of a system usingsatellites in random orbits.

One skilled in the art will readily understand that the drawings are notstrictly to scale, but nevertheless will find them sufficient, whentaken with the detailed descriptions of preferred embodiments thatfollow, to make and use the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The detailed description that follows is intended to provide specificexamples of particular embodiments illustrating various ways ofimplementing the claimed subject matter. It is written to take intoaccount the level of knowledge of one of ordinary skill in the art towhich the claimed subject matter pertains. Accordingly, certain detailsmay be omitted as being unnecessary for enabling such a person torealize the embodiments described herein. It will also be understoodthat terms indicating direction or orientation may be used facilitatedescription. The use of such terms does not imply that the claimedsubject matter is limited to a particular orientation of the structurebeing described.

I. Radio Mesh Concepts and Principles

The system described herein builds on certain principles underlying theuse of a plurality of transceivers (“nodes”) that can be used to formtermination points for links in a radio route using one or more of thetransceivers. Throughout the description herein, the term “radio,”“radio signal,” or the like is not limited to references toelectromagnetic radiation in frequencies commonly referred to as radiowaves. It is meant to encompass electromagnetic radiation of anyfrequency capable of transmitting information, including light,microwaves, VHF (“very high frequency”), UHF (“ultrahigh frequency”),etc. The discussion in this section describes certain relevant featuresof prior art arrangements sometimes referred to as mesh systems, andsome of the basic concepts that represent the significant advances overknown mesh technology achieved by the unique apparatus, systems, andmethods described herein.

A. Prior Art Mesh and Satellite Radio Communication Systems

Existing ground-based radio mesh systems such as those described in theinventor's U.S. Pat. Nos. 5,793,842 and 6,459,899 have proven veryeffective in establishing radio routes for digital and analogcommunication signals through a plurality of nodes. They are capable ofestablishing high quality radio links in a mesh system that allows nodesto be placed at convenient locations rather than in a predeterminedpattern. FIGS. 1A and 1B illustrate such a ground-based radio mesh. Inthis simplified example, communication signals CS can be transmittedbetween an originating node A and a nearby mobile radio (not shown),such as an Apple Inc. iPhone® or Samsung Electronics Co., Ltd., Galaxy®so-called smartphone. Those signals must be in turn communicated to a“drop,” such as a node B, which can be an Internet router or a telephonenetwork, for example, connected to a land line. If the nodes A and B arenot in line-of-sight contact because of the presence of an obstructionbetween them, such as a large hill LH (FIG. 1A), a direct radio link Lmay be subject to a severe reduction in signal strength, if it ispossible to establish a link at all.

As described above, many mesh systems proposed before those described inU.S. Pat. Nos. 5,793,842 and 6,459,899, used a central computer tocontrol routes between originating nodes and drops. However, the patentsdisclosed systems that utilized algorithms to enable the nodesthemselves to establish a preferred route between as many intermediatenodes as needed to optimize communications between an originating nodeand a destination node. For example, FIG. 1A shows a system in whichsoftware and firmware in the nodes themselves establish a preferredroute around the hill LH, comprising a radio link L1 between the node Aand a node X on top of a first high hill H1.

The nodes use a link L1 between nodes A and X, even though the linkactually leads in a direction away from the destination node B. Thealgorithms resident in the individual nodes then establish a radio linkL2 with another node Y on top of a second hill H2, and thence to thedestination node B. In this preferred route, a node Z in the mesh, whichmay be part of a radio route between two other nodes (not shown), isbypassed because the nodes X, Y, and Z self-determine that the preferredroute is through the nodes X and Y.

One of the important features of this system is that the nodesthemselves can also create a different preferred route, say between thenodes X and Y through a node Z using links L4 and L5, if conditionschange after placement of the nodes. FIG. 1B shows how the nodesthemselves can create a different route between nodes A and B if thereis no clear line of sight between them. In this example, the line ofsight has been interrupted by a building BL constructed directly betweenthe nodes X and Y. Another example would be a tree that permits radiosignals to pass between the nodes X and Y during the winter because ithas no leaves, but disturbs a radio link in the summer when its leaveshave come out. In such a case, the systems described in U.S. Pat. Nos.5,793,842 and 6,459,899 enable the nodes A, B, X, Y, and Z automaticallyto create a new preferred radio route using the new radio links L4 andL5 between the nodes X, Y, and Z.

These patents thus describe systems that use a mesh of nodes capable ofessentially random distribution in which the nodes themselves establishpreferred radio routes between destinations and drops using the onboardcomputational capabilities in the nodes to analyze radio signalsexchanged by the nodes. This eliminates the need for a central computerto communicate with the nodes and determine optimum or preferred routesusing data collected by the nodes from multiple other nodes in the mesh.Generally speaking, the only limitation on the placement of the nodes isthat intermediate nodes in a route of three or more nodes should bewithin sight of at least two other nodes. This allows the system tocover a wide area, and although it may require a large number of nodesto do so, as long as nodes can “see” each other the system will be ableto self-establish preferred radio routes.

However, it is not obvious how general concepts behind radio meshsystems comprising fixed-location, ground-based receiving andtransmitting nodes can be adapted to a system in which the nodes aresatellites orbiting the earth. The Motorola-Iridium system disclosed inU.S. Pat. Nos. 5,274,840 and 5,410,728 is more or less an analog ofground-based systems with nodes in particular locations. That is, itrequires the satellites to maintain predetermined orbits and haveonboard attitude control to keep the satellite antennas pointing in theright direction, and relies on knowing the locations of the satelliteswhen they receive a transmission from one ground station and retransmitit to another. While this approach works technically, it is believed tohave proved impracticable from a commercial standpoint because it wastoo costly to implement, although as noted above, it still has utilityin certain specialized applications. In addition, it uses a centralcomputer to establish radio routes among the satellites.

The inventor's U.S. Pat. No. 5,566,354 discloses a system usingrandom-orbit satellites, but as noted above, it is not actually a meshsystem as that term is used herein. For example, the system in the '354patent establishes a communication channel between ground-based mobileunits by having an originating unit send a page to a destination unit todetermine if a satellite is available for the purpose, and then simplytransmits communications between the two units through that satellite.The system does not have numerous salient features of the mesh systemdescribed herein, such as creating preferred radio routes using thequality of signals transmitted to and received by multiple nodes. Inaddition, the satellites still require expensive onboard attitudecontrol hardware such as positioning thrusters and rocket fuel for them,both of which add extra weight and thus increase the cost of deliveringthe satellites into orbit. The present system, on the other hand, usessatellites that continuously update the antennas in the nodes(satellites and ground stations) to enable a choice to be made as to theantennas at the nodes that will provide the highest quality radio linkbetween the nodes, whether they be satellites or ground stations. Inaddition, the '354 patent does not disclose how to providesatellite-to-satellite communications between randomly orbitingsatellites. And although the Motorola-Iridium system supportssatellite-to-satellite communications, its satellites have to maintainboth prearranged orbits and fixed attitudes.

B. Principles of the Unique Satellite Radio Mesh Systems DescribedHerein

The satellite radio mesh used in the present system supports radioroutes in which the preferred route between two ground stations includesmore than one satellite and having one or more satellite-to-satelliteradio links. It also supports radio routes that include a singlesatellite in communication with both ground stations. In bothembodiments a large number of unique satellites, described furtherbelow, are launched into orbit. The number of satellites is chosen toprovide a high probability that at any given moment, a point on thesurface of the earth will be within line of sight of a certain number ofsatellites. For example, U.S. Pat. No. 5,566,354 estimates that if 200satellites were randomly placed at an orbital altitude of 500 miles, agiven point on the earth would “see” on average over time about 12satellites, or stated another way, the chances of a given spot on theearth not being in the line of sight of at least one satellite is onlyfour in 1,000,000.

FIGS. 2A and 2B illustrate this principle graphically. The approximatedistance DH to the horizon EH from a satellite S at an altitude AL of500 miles can be calculated according to the formulaDH=[(R+500)²−R²]^(1/2), where R is the radius of the earth E. Dependingon the value chosen for R, DH is about 2000 miles. Thus, the area ofcoverage AR of a satellite is π×DH²≈12,500,000 sq. mi. Taking thesurface area of the earth as 197 million square miles, each satellitethus “covers” about 6% of the earth's surface, which means that onaverage any one point on the surface will “see” about 12 satellites(200×0.06). Conversely, the chance that a single satellite will not bevisible from any particular point on the earth is 94%. If there are 200satellites launched into random orbits, the probability that any givenpoint on the earth will not see at least one satellite is only0.94²⁰⁰≈0.0004% (that is, four in a million). The '354 patent includes atable, incorporated herein by reference, that shows the estimatedprobability of constant coverage over time of a point on the surface fordifferent numbers of satellites. It should be noted that the term“random orbits” in the context of the present description must beconsidered in combination with the number of satellites used in thesystem. It generally means that a sufficient number of satellites areplaced into orbits that are initially spaced apart with the goal ofmaximizing coverage of the globe. It is not meant to require randomdistribution in a pure mathematical sense. Rather, it is used toindicate that precise positioning of satellites at particular locationsis not required, and that the manner of placing them into orbit willtake into account the number of satellites comprising the system and thedesired degree of certainty, calculated in accordance with suitablestatistical algorithms, that any given point on the earth's surface willbe within sight of at least one satellite at all times. (It will beappreciated that the system permits different satellites to satisfy thatrequirement for a given point as the satellites' orbits change overtime.) For example, known techniques for generating so-calledpseudorandom numbers can be used as a basis for calculating initialsatellite numbers and placement. Other ways of achieving “random”satellite distribution are described in U.S. Pat. No. 5,566,354 in the“Satellite Launch” section, which is incorporated herein by reference.The number of satellites launched into orbit will preferably be inexcess of a calculated number to enable continued full earth coverage byaccounting for a certain number of satellite failures over time, or forsatellites that are destroyed by reentry into the earth's atmospherebecause of orbit decay or damaged by space debris.

Another important feature of the system described and claimed herein isthat the satellites do not require active, onboard attitude control.Thus, they do not require any moving parts, mechanisms, or propulsionsystems, which reduces satellite weight and cost, and they can bereleased into orbit without regard to their angular orientation. It isexpected that satellites can deployed from a launch vehicle such as aspace station or the like. It will be preferable in some embodiments ofthe system described herein to attempt to deploy them with as littleangular velocity as possible, but no special effort is required in thatregard. Systems in accordance with such embodiments will create radioroutes even if the satellites “tumble,” meaning that each satellite canchange its angular orientation at a rate different from othersatellites, or not at all, as it orbits. Stated another way, thesatellites are neither in prescribed orbits nor in controlledorientations. It is possible in some implementations to distribute themass of the satellites and/or components comprising ferromagneticmaterials to maintain a certain amount of tumbling as they orbit theearth and interact with its gravitational and magnetic fields. Inaddition, the size and orientation of solar panels used to produceelectrical power (see FIGS. 3 and 4) can be judiciously selected toemploy the kinetic energy of photons striking the panels to provideforces that influence the tumbling motion of the satellites. If desired,each satellite can include tracking telemetry to detect when its orbitis decaying and it needs to be replaced, and to comply with any nationalor international protocols applicable to orbiting bodies. However, it isexpected that it will be relatively simple and inexpensive to providesuch telemetry.

In another embodiment the satellites are deployed in random orbits withan angular velocity imparted to them. In the manner described furtherbelow, this enables the use of higher gain antennas to create beammatches even though the radio beams may be narrower. This enhances theability of the system to more readily create radio routes using morethan one satellite, which has the potential in some settings to increasethe quality of the routes between ground stations and thereby facilitatedata transmissions. It also increases the likelihood that a radio routecan be created between far distant ground stations that might bedifficult to connect via a system using tumbling satellites. Details ofthis embodiment are described in detail further below.

II. Satellite Design: Antenna Configuration and Onboard ControlCircuitry

The satellites according to one embodiment comprise system nodes thatutilize unique multiple antenna arrays and software-implementedalgorithms to create radio routes by enabling the nodes to nearlyinstantaneously identify an antenna transmitting information signals andan antenna in another node receiving information signals from thattransmitting antenna. Because the satellites and ground stations aregenerally equivalent vis-à-vis their function as nodes in the system,the term node can refer to both satellites and ground stations, unlessotherwise stated or the context indicates otherwise. In addition,software resident in each node uses content in the information signalsto evaluate the suitability of these antenna pairs as a radio linkbetween two nodes. Software resident in the nodes uses that evaluationto create a preferred radio route for sending data communications froman originating ground station to a destination ground station. Forpurposes of explaining basic concepts involved in creating radio routesusing the satellite system described herein, this discussion sometimestreats certain aspects of route creation separately. For example theconcept of identifying antenna pairs for potential radio links may bedescribed separately from identifying a preferred radio route selectingcertain links for a radio route. Nevertheless, it will be clear as thediscussion proceeds that route creation involves a combination of stepsthat begins when ground nodes send initial information signals andculminates with the creation of a preferred radio route forcommunication signals from an originating ground node through one ormore satellite nodes to a destination ground node.

The disclosed system and route creation process enables the use ofsatellites that drift in random orbits with no attitude control. Datacommunications can be transmitted and received even if the selected pairof antennas on the nodes changes over time, or if the satellitescomprising the route change over time. That is, computers onboard thesatellites and at the ground stations are capable of changing the radioroute during a given communication or from one communication to thenext. In addition, a radio route might utilize different satellitesduring a single communication. Or a first communication between groundstations at a first time could use a certain satellite or satellites,while a later communication between the same two ground stations mightuse one or more satellites not used in the first communication.

FIG. 3 is a schematic depiction of an embodiment of a satellite 10 thatcan be used in the space-based radio mesh systems described herein. Tofacilitate understanding of certain principles underlying the operationof the satellite 10 in the systems and methods described herein, it isshown with an outer casing 12 in the shape of a sphere centered at CT.Those skilled in the art will recognize that the satellite can have adifferent shape if so dictated by other design considerations. Certainfeatures of the satellite will be described with reference to acoordinate system having mutually orthogonal x, y, and z axes. It willbe understood as this description proceeds that one of the features ofthe space-based radio system disclosed and claimed herein is that thesatellite can assume any angular orientation as it orbits the earth, asalready discussed. It will be appreciated by those skilled in the artfrom the description thus far that the coordinate system shown in FIG. 3is used strictly for purposes of illustration in describing features ofthe satellite. Put another way, the coordinate system can be consideredto be tied to the satellite and to change its angular orientation withrespect to the earth as the satellite slowly tumbles.

The exemplary satellite 10 includes a plurality of antenna modules 12,one of which is depicted schematically in FIG. 3 for purposes ofillustration. Each antenna module in this example comprises adirectional antenna that transmits and receives radio signals at greaterpowers in predetermined directions. The present embodiment uses circulardish parabolic antennas each of which occupies a solid angle Ω with avertex at the center CT of the spherical satellite. The number ofdiscrete antenna modules incorporated into the satellite will depend onthe particular application of the system and the antenna design. In oneembodiment Ω in steradians will be chosen so that a particular number ofantenna modules, distributed around the satellite, will be capable oftransmitting radio signals to and receiving radio signals from asufficiently large spherical area to enable radio signals to be receivedfrom and transmitted to ground station transceivers and antennas inother satellites to effect operation of the system in the mannersdescribed below. The actual configuration of the antenna modules 12 canbe determined using known antenna design principles to achieve thatgoal.

However, fundamental principles of antenna operation demonstrate thetechnical feasibility of equipping a satellite such as that depicted inFIG. 3 with a sufficient number of antennas to effect the system andmethods described herein. One design approach could specify that thebeam width of the antenna for each module must provide a certainprobability that signals transmitted from all of the antennas in aparticular satellite will be received at another satellite or aground-based transceiver. A typical manner of expressing beam width fora circular dish parabolic antenna is the angle α at which the power ofthe beam has decreased by 3 dB. This is referred to as the half-powerbeam width (HPBW) and is given by the relationship:

$\begin{matrix}{\alpha = \frac{k \times \gamma}{d}} & (1)\end{matrix}$

where α is in degrees, k is a factor that depends on certain designparameters of the antenna and is typically assigned a value of 70°, γ isthe wavelength in centimeters, and d is the diameter of the circular“mouth” of the antenna reflector. Satellite Systems Engineering in anIPv6 Environment, Minoli, Daniel, CRC Press, Boca Raton, Fla. (2009),pages 78-80. For a 5 GHz signal, which is a common radio frequency(microwave C band) used in satellite communications, γ=6 cm (γ=c/f,where c=speed of light, 3×10¹⁰ cm/sec), so α≈140° for an antenna with adiameter d=3 cm. Under reciprocity principles, the same parabolicantenna would receive signals arriving at 70° off-axis at −3 dB of itson-axis gain. It will be appreciated that the design details of theantennas do not form a part of this disclosure. The principles ofoperation of the system as described herein will enable one skilled inthe art to select or design antennas that enhance the probability thatantennas on the random-orbit satellites will be able to establish radiolinks with other satellites and ground stations.

A satellite used in the present system will have to be large enough toaccommodate the various electronic and mechanical components requiredfor satellite operation, discussed below in detail in connection withFIG. 4, as well as being sufficiently robust in construction towithstand the stresses of launch and long-term exposure to the hostileenvironment it will encounter in orbit. It is expected that a satellitewith a diameter of 20 cm (approx. 8 in., about the size of a soccerball) will suffice, in which case the surface area of the sphericalsatellite 10 is 400π cm² (4π×(10 cm)²). The opening at the surface ofthe satellite for each antenna will be a size that permits the beam fromthe reflector below the surface to spread unimpeded. If the opening inthe satellite is a circle 6 cm in diameter, its area is 9π cm² (π×(3cm)²). Thus, the opening for each satellite will occupy 2.25% of thesurface area of the satellite (9π/400π). If 25 antennas were used, theywould occupy over 60% of the satellite surface.

It will be appreciated that satellites and antennas suitable for use inthe present mesh system can take different forms depending on trade-offsfamiliar to those skilled in engineering complex systems. As describedfurther below in more detail, one of the steps in creating a radio routeusing the embodiment of a satellite mesh described herein is thetransmission of identifying messages from all of the antennas in one ormore satellites and ground-based transceivers, which in certain contextsare referred to herein interchangeably as “nodes.” It will be seen thatincreasing the number of antennas in a node will increase the totalspherical coverage of radio signals transmitted from and received byother nodes, which in turn will increase the probability that a signalfrom one node will be received at another. It will be furtherappreciated that more antennas per satellite might make it possible toreduce the number of satellites placed in orbit. Such satellites mightbe more expensive and heavier, thus increasing launch costs, but otherfactors might offset the increased cost because fewer satellites mightneed to be launched. Those skilled in the art will also recognize thatthe system described herein can be implemented with satellites havingantenna arrays that transmit with less than full 360° sphericalcoverage.

By the same token, the increased weight of a ground station due toadding antennas is not a factor. Thus, a system might incorporatesatellites with fewer antennas than the ground stations. It might alsobe more feasible to design the satellites with a given number ofantennas and use statistical estimates to calculate the number of suchsatellites needed to ensure that a predetermined number is visible fromany given point on the earth's surface. After the satellites arelaunched into orbit, the system could be tested to confirm thecalculations and more satellites could added if desired. Moreover, thepresent example uses parabolic antennas to explain certain principlesinvolved in node design, but the system does not rely on using aparticular type of antenna. That is, the type of antenna and thespecific antenna design will also be factors in determining the beamwidth and number of satellites necessary to ensure to a suitableprobability that nodes will receive signals transmitted from other nodesat a useful gain. The factors that determine a successful design for anygiven implementation of mesh systems as described and claimed hereinwill be well understood by those skilled in the art.

The satellite 10 also includes a plurality of solar panels, three ofwhich 14 a, 14 b, and 14 c, are shown in FIG. 3. In the illustratedembodiment the solar panels are oriented in mutually perpendicularplanes and spaced equidistantly around the satellite 10. For purposes ofdescribing the locations and orientations of the solar panels in thisembodiment, a satellite equator 16 is defined as the great circle wherethe satellite surface is intersected by a plane parallel to the x-yplane and passing through the center CT of the sphere. A zero meridian18 is defined as the great circle where the satellite surface isintersected by a plane parallel to the x-z plane and passing through thecenter CT of the sphere. And a normal meridian 20 is defined as thegreat circle where the satellite surface is intersected by a planeparallel to the y-z plane and passing through the center CT of thesphere. The solar panel 14 a is attached to the satellite by suitablemounting structure 22 a at the intersection of the equator 16 and thezero meridian 18. The solar panel 14 b is attached to the satellite bysuitable mounting structure 22 b at the intersection of the equator 16and the normal meridian 18. And the solar panel 14 c is attached to thesatellite by suitable mounting structure 22 c at the intersection of thezero meridian 18 and the normal meridian 20.

The solar panels are generally planar with solar cells distributed overone or both faces for generating electricity when the solar cells areexposed to sunlight. For maximum effectiveness, the planar solar panelsare mounted in mutually orthogonal planes to ensure that an adequatenumber of solar cells are exposed to sunlight regardless of the angularorientation of the satellite. In the depicted embodiment, the solarpanel 14 a lies in the x-z plane, the solar panel 14 b lies in the x-yplane, and the solar panel 14 c lies in the y-z plane. It will also beappreciated that the satellite includes three more companion solarpanels where the equator, zero meridian, and normal meridian intersecton the other side of the satellite. The companion solar panels (depictedwith a prime (′) in FIG. 4) are preferably oriented in the same planesas each of their counterparts 14 a, 14 b, and 14 c shown in FIG. 3. Eachsolar panel is preferably normal to the surface of the satellite so thatit does not obstruct the transmission and receipt of radio signals byantennas adjacent to the solar panels.

It will be appreciated that FIG. 3 is intended solely to illustratefeatures of the satellite 10 necessary to an understanding of thepresent embodiment of the satellite mesh system described herein. Thoseskilled in the art will understand that an actual satellite forimplementing the present system may have design features not shown inFIG. 3's schematic depiction. For example, good design practice maydictate that the mouths of the antennas be recessed below thesurrounding surface of the satellite to reduce the possibility of impactdamage by space debris. Or additional protection might be provided bycovering each antenna mouth (recessed or not) with a sheet of materialtransparent to signals transmitted by and received at the satellite. Thedesign and placement of the solar panels 14 shown in FIG. 3 is alsohighly schematic, and the invention disclosed and claimed herein is notlimited to any particular solar panel configuration, placement, or meansof deployment.

FIG. 4 illustrates schematically various components housed by thesatellite 10 (node) for creating a radio route capable of transmittingand receiving radio signals to and from other nodes. As those skilled inthe art will readily recognize, in the descriptions of this and otherembodiments and aspects of the radio systems comprising the subjectmatter disclosed and claimed herein, the control circuitry andcomponents described and depicted in the various figures are meant to beexemplary of any electronic computer system capable of performing thefunctions ascribed to them. Such a computer system will typicallyinclude the necessary input/output interface devices and a centralprocessing unit (CPU) with a suitable operating system and applicationsoftware for executing program instructions. In addition, termsreferring to elements of the system, and of the user interfacesdescribed herein, are used herein for simplicity of reference. Forexample, the terms “component,” “module,” “system,” “apparatus,”“interface,” or the like are generally intended to refer to acomputer-related entity, either hardware, a combination of hardware andsoftware (firmware), software, or software in execution, unless thecontext clearly indicates otherwise. For example, such a component maybe, but is not limited to being, a process running on a processor, aprocessor, an object, an executable, a thread of execution, a program,and/or a computer. By way of illustration, both an application runningon an electronic computing device and the device itself can be acomponent. One or more components may reside within a process and/orthread of execution and a component may be localized on one computerand/or distributed between two or more computers.

Referring in more detail to FIG. 4, the satellite 10 is depicted in aview in the x-z plane in FIG. 3. It will be appreciated that FIG. 4,like other depictions used herein to describe the subject radio systemsand their components, is not to scale. It depicts the solar panels 14 aand 14 c, as shown in FIG. 3, as well as the diametrically opposedcompanion solar panels 14 a′ and 14 c′ mentioned above. It alsoschematically depicts a plurality of antenna modules 12 a, 12 b, 12 c,12 d, 12 e, and 12 f, representing all of the antenna modules onboardthe satellite 10, for transmitting and receiving radio signals asdiscussed above in connection with FIG. 3. This schematic depiction isintended to convey the principle of operation of the present embodimentwhereby the plurality of antenna modules in combination will be capableof transmitting and receiving radio signals to and from a node insubstantially all radial directions. (However, as already noted, thesystem described herein can also be implemented with satellites havingantenna arrays that transmit with less than full 360° sphericalcoverage.)

The satellite 10 includes a power module 30 capable of providing areliable source of electrical power for operating the components of thesatellite. The power module 30 includes batteries that are charged bythe electricity generated by the solar panels. Suitable power regulatingequipment provides steady-state power to the various electroniccomponents carried by the satellite even though the solar panels willspend one half of each satellite orbit out of sight of the sun. Inaddition to the power module the satellite includes a central processingunit 40 with an operating system module 42 that stores operationalsoftware for controlling the various functions of the satellite. Asshown in FIG. 4, the CPU 40 is operatively connected to all of theantenna modules 12 via power and data links 40 a, 40 b, 40 c, 40 d, 40e, 40 f, etc,

FIG. 4 also illustrates four main operational modules under the controlof the operating system module. These components are likewise includedin ground-station nodes. Each satellite node in a radio routenecessarily uses two antenna modules. Since the satellites have nopreferred orientation, it is necessary for each satellite (node) toselect antenna modules 12 to communicate with another node, either asatellite or a ground station. An antenna pairing module 44 under thecontrol of the operating system uses information messages received fromother nodes (ground stations or other satellites) to pair an antennamodule in one node for transmitting/receiving signals with an antennamodule in another node for receiving/transmitting signals. The radiosignals exchanged between nodes are analyzed by a route creation module46 that uses algorithms discussed further below to create a radio routebetween two ground stations. (Ground station nodes have correspondingcentral processing units.) Once a radio route has been established, adata movement module 48 within each node controls the transmission alongthe radio route of communication signals CS (see FIG. 1). As suggestedabove, the illustration in FIG. 4 of separate modules for antennapairing and route creation does not necessarily imply that identifyingantenna pairs for transmitting/receiving signals between nodes andselection of potential radio links as a radio route are other than partof a more or less unitary process of creating a preferred radio routefor transmitting data communications from one ground station to another.

III. Creating Radio Routes for Data Communications

Launching sufficient numbers of the satellites 10 in random orpseudorandom orbits as discussed above enables implementation of avariety of route creation strategies. This section will discuss twoembodiments, and variations thereof, of radio routes created using sucha satellite system. One embodiment creates a radio route that comprisesradio links between a single satellite and two ground stations. Anotherembodiment, which allows for communications over longer distances,creates a series of one or more subroutes comprising a first groundstation, a first satellite and a second ground station, and anothersubroute comprising the second ground station, a second satellite, and athird ground station, and if necessary a third subroute comprising thethird ground station, a third satellite, and a fourth ground station,and so forth. This radio route would enable communications between afirst ground station and an n^(th) ground station using n−1 satellites.Variations on these embodiments are discussed below as well. Forexample, those skilled in the art will understand that a radio route canalso include satellite-to-satellite links if the computers resident inthe nodes assemble such a route based on the principles discussed below.

The ability to transmit data between ground stations using radio routesaccording to this embodiment of the present system is essentiallyconfirmed by the known operational capability of the Motorola-Iridiumsystem, which uses fixed satellites with attitude control. That type ofsystem was able to establish communication links directly betweensatellites and hand-held units on the ground in spite of the limitedantenna power (or gain) available in such units. Thus, an embodiment ofthe present system that uses antennas with limited power in thesatellites in combination with ground stations having more powerful,different type, and/or a greater number of antennas is virtually assuredof being able to establish radio routes between two ground stations.

A. Two Ground-Station/One-Satellite One Satellite Radio Route

A basic embodiment of a satellite mesh system according to the presentinvention uses one of the satellites in accordance with the abovedescription to create a radio route for communications between twoground stations. This route involves two radio links, one between afirst ground node and a satellite node, and the other between thatsatellite node and a second ground node. Although the configuration of aground station may be different from that of the satellites,conceptually the transmission and reception of radio signals areprocessed by each essentially the same way. The creation of radio routesmay be enhanced by ground station nodes using more and/or more powerfulantennas, as well as different antenna types, as compared to thosecarried by the satellites, since the nodes on the ground do not have thesame constraints on weight, power, and space limitations as thesatellites. In addition, the ground station antennas can be mounted ontall buildings, towers, high hills, etc., to maximize line-of-sightvisibility with the orbiting satellites. In addition, the ground nodesonly transmit throughout a hemisphere, rather than in all sphericaldirections like the satellite nodes, thus reducing the cost of addingantennas for enhanced link creation.

1. Radio Route Creation and Maintenance

The principles underlying creation of radio links in the satellite meshsystems described herein will first be described by using a paradigm inwhich all transceivers, both satellites and ground stations, areconsidered to be nodes in the mesh. This will enable an understanding ofhow a radio route is created with more than one node-to-node link (thatis, with at least three nodes). Creation of a radio link betweensatellites or a radio link between a satellite and a ground station isin most relevant respects the same. Identifying and optimum radio linksand routes between pairs of nodes is in some ways analogous to themanner in which routes are created in the ground-based system describedin the inventor's U.S. Pat. Nos. 5,793,842 and 6,459,899. Thedescription of link selection and route creation in those patents isincorporated herein by reference for background information regardingoptimum or preferred route creation by the nodes in a radio mesh.

An important difference, though, is that the present system, unlikethose known in the prior art, creates routes using nodes the positionsand orientations of some of which (the satellites) change over time.Accordingly, while prior fixed-node systems might occasionally have tochange a radio route for reasons discussed above in connection with FIG.1, they did not involve a dynamic environment with moving and tumblingnodes that required the system to be capable of automatically anddynamically updating the selection of transmitting/receiving antennapairs in the nodes as they move relative to each other and changeattitude. For example, Motorola-Iridium systems used satellites withfixed attitudes and known relative positions, thus making possibleoptimum route creation in a manner known for ground-based systems(although the Motorola-Iridium system is not known to use the nodesthemselves to create radio routes).

As just indicated, the present system and method for creating a radioroute with robust radio links between nodes involves selecting pairs ofantennas and estimating the “quality” of each link by criteria discussedbelow. An explanatory example will be described in connection with FIG.5, which shows a plurality of satellites with address nos. 140, no. 250,no. 280, no. 300, and no. 165, which can form radio links with groundstations with addresses no. 1000, no. 1052, no. 1630, and no. 2001. Thefollowing explains how the just the nodes in the system determine apreferred radio route for data communications (calls) from ground nodeno. 2001 to ground node no. 1000 by choosing between two potentialroutes, one via satellite no. 250 and the other between satellite no.300. In a typical system there will be about 200 satellites. The numberof ground stations can vary, of course, but FIG. 5 illustrates a fewsuch ground stations over a wide area about, say, 700 miles in diameter.

The link selection process is begun by transmitting from each groundnode a routing signal in the form of an initial information signalcomprising an identifying packet with the initial information. Theantenna modules in every node, both satellite nodes and ground nodes,are each given an identifying number, In addition, each node isidentified as either a ground node, sometimes referred to as type A, ora satellite node, sometimes referred to as type B. This node identifyingdata will typically be contained in a packet header, and the identifyingpacket will include a payload comprising an initial sample data stream.The following Table 1 is an example of digital first information signalstransmitted from two of the antenna modules in a first sending groundnode, say the node assigned address “1000.”

TABLE 1 Packet No. 1 Node address no. 1000 Node type: A Node antenna no.GA1 Link count:   1 Sample data (payload) XX . . . XX Packet No. 2 Nodeaddress no. 1000 Node type: A Node antenna no. GA4 Link count:   1Sample data (payload) XX . . . XX

Similar packets will be transmitted continuously from all of theantennas in all of the ground nodes. These signals will be received by anumber of other nodes, both ground stations and satellites, but theantenna pairing modules in the nodes will reject information signalssent from the same node type. The satellites also store the number oflinks back to the sending ground node. In this case, the link count isone.

The initial sample data stream will typically be a known sequence ofbits used to evaluate the quality of a potential radio link between twonodes in a manner described just below. It is anticipated that theantennas in each node can transmit the information signals at randomintervals without encountering interference with information signalstransmitted from other nodes. This is because the number of nodes, andthe number of antennas in a given node, that will receive signals fromother nodes will likely be small. Alternatively, the antenna modules inthe nodes can transmit information signals in preassigned time slots tominimize even further the possibility that an information signaltransmitted from one node will arrive at a given antenna in another nodeat precisely the same time that the given antenna is transmitting itsinformation signal.

Continuing with this example, the second step in the process involves anevaluation by all of the satellite nodes that receive initialinformation signals from the ground nodes. The process involves aplurality of operations carried out in the satellite antenna pairing androute creation modules. The antenna pairing modules in the receivingsatellites store the antenna on which it received the initialinformation signal. In the FIG. 5 example, satellite no. 250 storessatellite antenna SA6 associated with ground node address no. 1000, andsatellite no. 300 stores satellite antenna no. SA3 associated withground node address no. 1000. The route creation circuitry determines afigure of merit of the received initial information signal that reflectsa quality of the signal transmitted over that pair of antennas in therespective ground station and satellite. The figure of merit resultsfrom an analysis of certain parameters according to algorithms in thenodes, its purpose being to assign a quantitative value for ranking thesuitability of particular antennas in the two nodes as a radio link inthe radio route to be created between an originating ground station anda destination ground station. That is, this step in the process involvesranking the quality of a potential radio link between a ground stationsending an initial information signal and a satellite receiving it.Examples of properties of received signals that can be used to derive afigure of merit (signal quality) are one or more of signal strength, theerror rate in the data stream, and signal-to-noise ratio. In thisexample, the figure of merit ranges from one (worst quality) to 10 (bestquality).

The next step is for the route creation circuitry in all of thesatellites to send routing signals in the form of linking informationsignals from all of their antennas. To illustrate, assume that satellitewith address no. 250 receives an initial information signal from sendingground node no. 1000. Table 2 shows the linking information sent inpacket form from every antenna in node no. 250 vis-à-vis a potentiallink with sending ground node no. 1000:

TABLE 2 Transmitting from: Node No. 250 Node type: B Node transmittingantenna no. SA1 Node receiving antenna no. SA6 Linking node address no.1000 Linking node antenna no. GA1 Link count:   2 Link figure of merit(FOM) 6 of 10 Sample data (payload) XX . . . XX

Table 3 shows the linking information sent in packet form from everyantenna in node no. 300 vis-à-vis a potential link with sending groundnode no. 1000:

TABLE 3 Transmitting from: Node No. 300 Node type: B Node transmittingantenna no. SA4 Node receiving antenna no. SA3 Linking node address no.1000 Linking node antenna no. GA10 Link count:   2 Link figure of merit(FOM) 3 of 10 Sample data (payload) XX . . . XX

The linking signals will not be accepted at other satellites, which arethe same type (type B) as the satellites no. 250 and no. 300 sending thelinking message. In addition, the ground nodes will be programmedlikewise to reject linking signals with a linking node address the sameas the receiving ground station. Note also that the link count fromTable 1 is incremented by one by the satellites, reflecting the numberof links (two) to the sending ground node no. 1000.

The antenna pairing circuitry in a receiving ground station thatreceives a linking signal stores at least the satellite node addressesfrom which the linking signals were transmitted, as well as the antennaon which the linking signals were received at the receiving ground node.In FIG. 5, the ground station no. 2001 stores satellite address no. 250associated with antenna no. GA5, and satellite address no. 300associated with antenna no. GA21. The receiving ground node alsodetermines respective figures of merit for potential links betweenitself and satellite no. 250 and between itself and satellite no. 300.In this example, the FOM=6 for a potential link between ground stationNo. 2001 and satellite no. 250 and FOM=8 for a potential link betweenground station No. 2001 and satellite no. 300.

A preferred radio route between from the receiving ground station to thesending ground station is then determined based on the figures of meritof the available potential links. In the example shown in FIG. 5, thetotal figure of merit for the radio route via satellite no. 250 is 12(6+6) and the total figure of merit for the radio route via satelliteno. 300 is 11 (3+8). Therefore, the preferred radio route is viasatellite no. 250. Note that it is the quality of the overall route thatdetermines the choice, not the quality of an individual link. Asdescribed in more detail below, a data transmission destined for thesending ground station no. 1000 includes the destination address (nodeno. 1000). The receiving ground station no. 2001 knows that the firstradio link in the route to destination node no. 1000 is satellite no.250 and that a transmission on antenna no. GA5 of ground station no.2001 will be received at satellite no. 250. (Optionally, the satelliteno. 250 can confirm that the transmission is from ground node no. 2001if the transmission is received on satellite antenna no. SA1.) Satelliteno. 250 has stored antenna no. SA6 as the antenna to use for datatransmissions to ground station no. 1000. (Optionally, the groundstation no. 1000 can confirm that the transmission is from satellite no.250 if the transmission is received on ground station antenna no. GA1.)Thus, the selected antennas at the ground stations and the satellite(the nodes) direct transmission signals from an originating node to asatellite and then to a destination node without requiring that theentire route being stored at any one node or central location andwithout requiring a central computer to determine a preferred route.From this example, one skilled in the art will understand how radioroutes are constructed for data communications from any of multiplereceiving (destination) ground stations to any of multiple sending(originating) ground stations.

It will also be understood that the satellites no. 140, no. 280, no.165, etc., may also receive initial information signals from the groundstation no. 1000 and send linking signals that are received by groundstations no. 1052, no. 1052, no. 1630, and no. 2001. Likewise, all ofthe satellites shown in FIG. 5 and any others within radio range (seeFIG. 2) may receive initial information signals from all of the groundstations no. 1052, no. 1630, and no. 2001, and any others within radiorange. However, the determination of a preferred route between any twoground stations proceeds according to the above discussion, in which thecombined figure of merit of both potential links in a radio routebetween the ground stations is evaluated by the receiving ground node ofa potential radio routes.

The above steps are continuously repeated at predetermined intervals,including during the transmission of packets of communication signalsover a radio route. Thus, as the satellites move and change orientation,the modules in the nodes can continuously update the evaluation of theradio links between nodes, and can change the preferred radio routebetween originating and destination nodes. This is facilitated by thefact that each node actually only communicates with a limited number ofother nodes and thus only a limited number of links has to be updatedwith each iteration of the link creation process. The frequency of thelink refreshing process will depend on various factors, but it isbelieved that frequencies between 0.5 and 20 Hz will be adequate in atypical system. As already noted, the link selection and maintenanceprocedure is performed by computations solely using the onboardcalculating capacity of the nodes as described herein.

It should be also noted that one node might receive a signal fromanother node on more than one antenna, depending on the properties ofthe antenna modules, such as their HPBW. However, the route creationprocess is the same as described above in that instance. It will also beappreciated that many different criteria can be used to evaluate thequality of the potential link between the nodes. Typical ones would bedirect indications of link quality such as the strength of the receivedsignal and the error rate estimate. However, other criteria can be usedas well. For example, the amount of remaining battery life in each ofthe nodes in the potential link could be determined and the qualityrating (figure of merit) adjusted to account for how long a satellitehas been exposed to the sun as an indication that battery power mightonly remain strong enough to support a link for a short time. Anothercriterion could be link loading, which refers to the number of potentialradio links with other nodes that is stored at a particular node. Eachnode in the system (ground stations and satellites) can eliminatepotential links with a quality below a predetermined threshold (sayFOM=2). This will prevent a route from being formed using one very highquality link and one very low quality link, the latter of which maydisrupt data communications even though the overall quality of the routeappears to be satisfactory. It may also reduce the time required todetermine a preferred a radio route by eliminating a number oftransmissions between the nodes.

2. Transmitting Data Communications over the Radio Route

As just explained, once a plurality of links is assembled into a radioroute, it can be used to transmit communication signals from anoriginating node to a destination node. However, one issue that must beaddressed when communicating data transmissions over the radio route isthat a single antenna in a node cannot both transmit and receive signalssimultaneously. This issue is addressed in a variety of ways in the '842and '899 patents. One that is particularly adapted to the present systemis the designation of the nodes as one of two types, called “A” and “B”in this description (or “odd” and “even” in the '842 and '899 patents).In such an arrangement signals transmitted from one type of node areseparated in some fashion from signals transmitted from the other typeof node so that a node can receive signals on the same antenna that ituses for transmitting signals.

One way of doing this is for one type of node to transmit in certainfrequency bands and the other type to transmit in different frequencybands. In this arrangement an antenna in a node can transmit and receivesignals at the same time. One drawback is the necessity of providingsufficient separation between the respective frequency bands to ensurethat the there is no interference when an antenna is transmitting andreceiving at the same time. Another way of separating signaltransmission and reception is to transmit from one type of node in aparticular time slot and from the other type of node in a different timeslot interleaved with the first time slot.

Data/communication signal transmission in accordance with thisdescription is controlled by the data movement modules 48 in thesatellites 10. For example, a data communication comprising packets ofdata with a header and a payload will be received at an originatingground station. The header will typically include address information,including identification of the destination ground station. The datatransmission module unpacks the address information and indicates thesystem address (node number) of the destination node. The packets willthen be sent to the destination ground station over the radio routeestablished in the manner described above. An important aspect of thepresent system is that the preferred radio routes are subject to changeeven during an ongoing data transmission. However, the data packetsarriving at the destination ground station can be unpacked, undergoerror correction, and be reassembled in the proper order in accordancewith known principles, even if the packets arrive out of order becausethey traveled via different routes or were delayed while a differentroute was being created.

3. Summary

It will be apparent to those skilled in the art that the present systemis not simply a superposition of the route creation techniques describedin the '842 and '899 patents on a three-dimensional mesh in which thenodes include satellites instead of fixed devices in an essentiallytwo-dimensional space. There are numerous factors that go into linkselection and route creation, some of which are discussed above, thatmust be accounted for in the type of space-based, three-dimensional meshdescribed herein. For example, since the satellites have differenttrajectories, some of which will pass over large expanses of unpopulatedoceans, while others will pass over land masses that will generate moredata transmissions, battery life can vary greatly from satellite tosatellite. Accordingly, the amount battery charge remaining can be animportant parameter in selecting a satellite as a node in a radio route.

The use of a single satellite to establish an optimum or preferred radioroute has several advantages. One is that it identifies a preferredroute virtually instantaneously because the radio signals passed betweenthe satellites and the ground stations include information that is usedby algorithms stored at the ground stations and in the satellites tocalculate a preferred radio route in small fractions of a second. Thus,as soon as a ground station transmits a signal indicating that a routeis needed to another ground station, the route can be establishedimmediately and used for transmitting communication signals. This typeof three-node route can “refresh” sufficiently rapidly to minimizedisruptions of data transmissions so that if at a later time a differentsatellite, or different antennas on the same satellite, would provide abetter quality route, the route configuration can be adjusted nearlyinstantaneously to provide better quality links and minimize delays indata transmission. It also allows for changing the satellite used in theroute for other reasons, an example being waning battery life.

Those skilled in the art will understand that engineering a system inaccordance with the above description will require trade-offs amongdifferent aspects of the system. Thus, an actual system will likelyinvolve many competing considerations in optimizing a particular design.Some of these considerations are the number of satellites, satellitealtitude, the number of antennas, particularly in the satellites, thebeam width of the antennas, the size of the satellites, the cycle timefor updating route creation, just to name a few.

B. Examples of Radio Routes Created Using the Present System

An aspect of the present embodiment is that the probability of therebeing at least one satellite present to establish aground-to-satellite-to-ground radio route can be readily increased bysimply placing more satellites in orbit, in accordance with thedescription above. Since the satellites are very light and inexpensive,increasing their number is an economically feasible way of increasingthe reliability of the system. Although there may be periods when thereis no satellite immediately available for the establishment of a radioroute between two ground stations, the rapid rate at which the systemcan refresh itself increases the probability that at least one satellitewill soon (likely within a few seconds) become available. In mostapplications, a time lag with a duration of this order of magnitude willbe acceptable. For those reasons, a particularly useful application ofthe present embodiment is providing reliable radio routes overparticular geographic areas.

1. Establishing a Single-Satellite Route in a Particular Geographic Area

FIG. 6 illustrates an application of this aspect of the invention inwhich the plurality of randomly orbiting satellites is used to create aground-to-single-satellite radio route over which signals can betransmitted and received only over a predetermined geographical area.The example presented here is a system for transmitting and receivingcommunication signals throughout the country of Egypt. FIG. 6 is a mapof Egypt that shows a coverage area CA in which a single satellite isused to effect communications between Cairo and the southwest corner SWof the country. As above, the system includes 200 satellites. The circlesegment labeled CO indicates an area in which a satellite will seeCairo. The circle segment labeled SW indicates the area in which asatellite will see the southwestern corner SW of the country. The areaCA represents the overlap of these circles, signifying the area whereboth Cairo and the southwest corner SW will see the same satellite.

The area CA of the overlapping circles CO and SW is given by thefollowing relation:

${CA} = {{2{DH}^{2}{\cos^{- 1}\left( \frac{m}{2{DH}} \right)}} - {\frac{m}{2}\left( {{4{DH}^{2}} - m^{2}} \right)^{\frac{1}{2}}}}$

where m=700 miles, which is the distance between Cairo and SW, and DH isthe distance to the horizon from a satellite (see FIG. 2). Accordingly,the area CA in which a single satellite will enable communicationbetween ground stations at Cairo and the southwest corner SW is about9,800,000 sq. mi. By the calculation above in connection with FIG. 2,the coverage area CA is about 5.0% of the earth's surface. If there are200 satellites in random orbits per the present description, there willbe on average at least 10 satellites visible from any point within thecoverage area. Stated another way, the probability that at least onesatellite will not be available for communication between Cairo and SWis only 0.95²⁰⁰≈0.0035% (or about 35 in a million). In an actualimplementation the area will be somewhat less because the closer asatellite is to the horizon for a particular location, the less likelyit is to be able to receive radio signals from a ground station at thatlocation due to atmospheric effects or interference from nearbybuildings or topographical features such as mountains or the like. Theability of a ground station to see satellites near the horizon can beimproved by placement of the ground nodes on high towers or hills ortall buildings. Since ground stations will typically use utility power,there is normally little or no constraint on the power available atground stations. In addition, the ground stations can utilize antennadesigns that increase weight, while in the satellites the goal isgenerally to reduce weight to minimize launch costs. In other words, theengineer designing the system would have much more flexibility inconfiguring the ground stations to increase their effective range andthus make more satellites available for single-satellite route creationthan might otherwise be available if the ground stations had the sameantenna modules in the same numbers as the satellites.

FIG. 6 uses the dotted circle segments to indicate the coverage area forcommunications with other ground stations, such as the northwest cornerNW and southeast corner SE of the country. For example, a satellitewould have to occupy the overlap between the two circles labeled NW andSE for communications between ground stations at those locations. Statedanother way, any single satellite within that area would support a radioroute between those ground stations. As another example, any satellitewithin the overlapping area of two 2000-mile radius circles centered onCairo and SE would support a radio route between ground stations atthose two locations. The same principle applies to communicationsbetween two ground stations located at Cairo and NW, and so forth.

A radio route is established between two ground stations (say at Cairoand near SW) in the manner described above for establishing radio linksbetween nodes. While in the present embodiment a given radio route willonly include a single satellite because all satellites are nodes of onetype and all ground stations are nodes of a different type, the routeneed not necessarily comprise only a single satellite. Nevertheless, itis expected the route creating modules in the nodes will inherentlyfavor single-satellite radio routes because they will likely provide apreferred route in terms of the collective figures of merit of the linksin such a route. In addition, a radio route is maintained between thetwo ground stations even if the satellite originally used to create theroute disappears over the horizon and from the view of one of the twoground stations (see FIGS. 2A and 2B). In that case, the computersaboard a different satellite in view of both ground stations can be usedto create a new radio route. During the brief times that couldtheoretically occur when no route is available, the transmission data isstored in a buffer memory until a route is available. As noted above,the communication data packet headers include sequence information thatpermit them to be reassembled in order at the destination node fortransmission to a user connected to the destination node via a landlineor WiFi.

2. Single-Satellite Routes With Wide Area Coverage

FIG. 7 plots the general relationship between the distance separatingtwo ground stations and the area in which two circles centered onrespective stations overlap with each other. If the two points are about700 miles apart (as in the example above using Egypt), the overlappingarea CA of two circles with a radius DH of 2000 miles is about 78% ofthe area AR (FIG. 2). As the distance increases, the overlapping areacorrespondingly decreases. FIG. 7 shows the overlapping area LA of twocircles centered on New York and Los Angeles. That area is about3,400,000 sq. mi., which is only 27% of the area AR covered by a singlesatellite. This represents only 1.7% of the earth's surface of197,000,000 sq. mi. For a system comprising 200 satellites, there onlywill be about 3 or 4 satellites visible from both cities. Consideringthat the Rocky Mountains will intercept westward signals toward LosAngeles at shallow angles to the earth's surface, there may in fact beno satellite capable of communicating with both cities for long periodsof time. Russia presents an even more extreme situation. The distancebetween Vladivostok and St. Petersburg is about 4000 miles, meaning thatin no case will a single satellite be capable of providing a radio routebetween them. Even cities closer together in Russia may not present asufficiently large probability of establishing a single-satellite radioroute between them if they are on opposite sides of the Ural Mountains.

The single satellite embodiment of the invention is readily adapted tosettings where ground nodes are too far apart, or where topographicalfeatures will severely limit the number of satellites visible to bothground nodes. In that case one or more intermediate ground nodes areprovided between the distant locations. The intermediate ground stationswill appear to the system just like the satellite nodes. To illustratethe point, consider a system in which ground nodes are located at NewYork, Kansas City, and Los Angeles. The route creation algorithms in thesatellites visible to the New York/Kansas City ground nodes willdetermine a first preferred radio route segment and those in thesatellites visible to Kansas City/Los Angeles ground nodes willdetermine a second preferred radio route segment in series with thefirst. Although the route will not necessarily be constrained tocomprise two single satellite route segments (New York/Kansas City andKansas City/Los Angeles), it is believed that will typically be the endresult. The link count discussed above could be used as a factor inselecting the preferred radio route between two distant ground stations,which in some circumstances could result in a single satellite radioroute.

However, the system will be free, as discussed, to create a route, say,between New York and Los Angeles using a single satellite, or anintermediate satellite/satellite link if the route creation computers inthe nodes so dictates. Satellite-to-satellite links can be establishedif a sufficient number of satellites of the same “type” as the groundstations are placed into orbit. These satellites would function as akind of blind node that could only be used for communications betweensatellites of the other type but not with ground stations. It isexpected that a limited number of such blind node satellites would berequired because of the great distances over which orbiting satelliteswould able to see each other.

3. Additional Properties of Single Satellite Radio Routes

One property of the mesh system described herein is the ability torestrict data communications to particular ground stations. For example,if security concerns required that certain communications from a groundstation only be capable of transmission to one or more other groundstations, the packet header could include encrypted information thatcould only be decoded by a ground station with a suitable decryptionkey. The communication could be double encrypted by including anencryption key in the information signals used to create radio links aswell as in the data communications themselves. The same principle couldbe used to prevent communications to certain ground stations in general.For example, in the example above relating to a system deployed forcommunication between ground stations in Egypt, data packets sent from aground station could include an address field permitting the creation ofradio routes only with other ground stations in Egypt. This type ofsingle or double encryption could also be employed by a country forpolitical or religious reasons.

IV. Rotating Satellites

As already discussed, designing a satellite-based radio mesh system inaccordance with the above description involves myriad trade-offs among awide variety of parameters. Two particular parameters that work at crosspurposes, and thus require judicious selection, are the beam widths ofrouting signals and calls transmitted by the antennas in the nodes andthe power (gain) of the antennas. On the one hand, greater beam widthwill increase the probability that a beam match can be created, but agreater beam width reduces the gain of the antenna. Conversely, anarrower beam will increase antenna gain, but reduce the probability ofcreating a beam match between nodes. This trade-off is particularlysignificant in the satellite nodes because the satellite antennaconfiguration has to take into consideration constraints on the weightand size of the satellites, which limits the number of antennas thesatellite can carry, and on the electrical power available from onboardbatteries. It is also desirable to increase the number of possible beammatches between nodes because some radio beams may be weakened bygrazing the earth's surface, which can partially block the signal beforeit reaches a receiving node.

Achieving the proper trade-off between beam width and antenna gain isimportant to the efficient functioning of a random-orbit satellitesystem. Such a system relies on the statistical probability that routescan be created using randomly orbiting satellites to create and selectroutes. A basic system that is simple and inexpensive to implement, andis especially effective in creating single satellite radio routes, usestumbling satellites as discussed above. As already described, thesatellites' antennas point out into space—towards each other and theearth—to enable the establishment of links between nodes. A fundamentalproperty of the system is its dependence on routing signals and datatransmissions of sufficient strength reaching other nodes (groundstations and satellites). The system relies on having enough satellitesin orbit and making the proper design trade-offs, including beam widthvs. gain, to enhance the probability that a suitable route can becreated between two ground stations via one or more satellites. However,there may be system installations in which better data transmissioncould be achieved by a multiple satellite route if the probability ofcreating high quality (figure of merit) links between satellites isincreased.

The present embodiment utilizes satellites that rotate about an axis,which, as explained herein, increases the likelihood that a route withhigh quality links and sub routes can be created using one or moresatellites. As explained below, employing rotating satellites enablesbeam width to be reduced, with a corresponding increase in gain, therebyresulting in higher quality radio links between nodes.

A. Principles Underlying the Present Embodiment

In the tumbling satellite embodiment discussed above, an exemplarysatellite configuration uses 25 antennas covering about 60% of thesurface of a spherical satellite. Thus, a rough estimate of theprobability of a radio beam transmitted by such a satellite beingreceived by another like satellite would be about 36% (0.6×0.6). It willbe appreciated by those skilled in the art that this is only anestimate, since the radio beams will have side lobes that will increasethe probability that a link will be created to a certain extent. If thediameter of the satellite is doubled, the diameter d of the parabolicdish antennas used in the above-described example can also be doubled.By above equation (1), α=(k×γ)/d, the HPBW will be halved, to 70°, fromthe value of the antenna example given above. While the area of the beamwill be only ¼ as large, the antenna gain will be increased by a factorof four, or about 6 dB. On the other hand, the probability of a radiobeam transmitted from one tumbling satellite being received by anotheris reduced to about 2% (36%×(¼)²).

As discussed above in the tumbling satellite embodiment, repeated radiosignals sent by nodes in the system include information on links and subroutes that need only include the address of a final ground destinationand a figure of merit to that destination. The rotating satelliteembodiment takes the tumbling satellite embodiment as a point adeparture toward a technique for increasing the likelihood of creating aradio link, especially between satellites with high-gain, narrow-beamantennas. It will be appreciated, particularly from the discussion thatfollows, that a particular radio route in a spinning satellite systemmay not last as long as in a tumbling satellite system. Accordingly, oneway to enhance the route creation process would be to use route creatingsignals that have a smaller amount of sample digital data (see Tables1-3, above) to enable them to be transmitted in a shorter period of timeto effect more rapid route creation.

As also discussed above, data transmissions (“calls”) will typically bein the form of packets with a header, which includes address dataindicating the packet destination, and a payload comprising the contentof the transmission. Header information in multiple packets can be usedto arrange the packets in the same order in which they were transmitted.Although a particular radio route in a rotating satellite system may notlast as long as in a tumbling satellite system, the data transmissionpacket headers will include information on the proper order of thepackets for use by the destination ground station to reassemble thetransmission. Thus, while there may be delays in completing a particulardata transmission while a new radio route is created inmid-transmission, that potential drawback will be offset by the factthat the higher gain radio beams made feasible by using rotatingsatellites will be more likely to establish radio routes by which datatransmissions between certain ground stations can be made in the firstplace.

B. Linking Satellites to Satellites

The discussion further above of the tumbling satellite embodiment pointsout that the establishment of radio links between ground stations andsatellites can be enhanced by increasing the number and gain of groundstation antennas. This is feasible in most installations because groundstations typically do not have the constraints on weight, availablespace, and electrical power that exist with the satellites. In thepresent embodiment the establishment of radio links by beam matchingbetween satellites is enhanced by using satellites that are deployedinto orbit deliberately spinning about a rotational axis. In oneembodiment, the satellites themselves have the same components as thesatellite depicted in FIGS. 3 and 4 and described in the text aboveassociated with them.

The angular velocity of the satellites will be relatively high. Forpurposes of illustrating the operation of a typical system usingrotating satellites, it will be assumed that the satellites are deployedwith an angular velocity ω=2π rad/sec (60 rpm). Those skilled in the artwill understand that this example is not meant to be limiting and thatit is within the scope of this disclosure to employ any angular velocityeffective to establish radio routes as described and claimed herein. Theorientation of the axis of rotation will not be controlled, butprinciples of physics dictate that each satellite will assume an axis ofrotation through its center of mass and the axis of rotation willprecess around the angular velocity ω. However, the orientation of theaxis of rotation at any given time does not affect the creation of radiolinks, as will be apparent from the discussion that follows.

Rotating satellites increase the probability of a transmitted radio beambeing received by another satellite because the satellite antennas“sweep” an area as the satellite rotates. This can be understood byconsidering the satellite S₁ shown in FIG. 8A, which is schematiccross-section through the satellite “equator,” corresponding to theequator 16 of the satellite 10 in FIG. 3. In this example, the satelliteS₁ comprises five antennas 12 ₁, 12 ₂, 12 ₃, 12 ₄, and 12 ₅, each havingan HPBW of 70°, arranged equally around its equator 16 and rotatingabout the z-axis at an angular velocity cu. A location RL remote fromthe satellite and lying in the plane of the equator will “see” fiveantennas as the satellite rotates through one complete revolution. Itwill be understood that this number will be different for locations notin the equatorial plane, but the principle still holds. It will also beappreciated that the number may increase or decrease because ofprecession about the rotational axis, but most locations remote from thesatellite (including ground stations) will still see plural antennas asthe satellite rotates. Thus, a second satellite with its equatorialplane in the equatorial plane of the first satellite S₁, the probabilityof being able to create a radio link with a 6 dB gain increase over thetumbling satellite example above is about 10% (5 antennas×2% for eachantenna). The probability of creating a beam match with a ground stationantenna is likewise increased.

It will be understood that this is a highly idealized representation,which ignores factors such as precession of the satellites around theiraxes of rotation, but it nevertheless illustrates the concept thatrotating satellites present an increased probability for the creation ofbeam matches between two satellites. Nevertheless, considering the largenumber of randomly orbiting satellites available for route creation, theincreased probability of beam matches using rotating satellites will inmany, if not most, cases be sufficient to enable assembly of a radioroute with higher quality links between two ground stations via multiplesatellites. While this will have special applicability in reachingground stations separated by large distances, it also can increase thereliability of radio routes between ground stations in other settings.

1. Counter-Rotating Satellites

The satellites are preferably deployed with about half of them rotatingin a first direction about their rotational axis and the other halfrotating in the opposite direction. FIG. 8B, which uses like numeralsfor like parts in FIG. 8A, illustrates this principle by showing thesatellite S₁ rotating at an angular velocity ω in a first direction anda second satellite S₂ rotating at the same angular velocity −ω (in theopposite rotational direction). This illustrates how a beam matchbetween antenna 12 ₅ in satellite S₁ and antenna 12 ₄ in satellite S₂will be sustained longer than if the two satellites were rotating in thesame direction. That is, if the satellites are rotating in oppositedirections, facing antennas on the satellites are traveling atessentially the same linear velocity relative to each other. On theother hand, if the satellites are rotating in the same direction, theirrelative linear velocity is twice the linear velocity of each. With asufficient number of satellites in orbit (200 in the previousembodiment), it is believed that there is a significant probability ofhaving a plurality of counter-rotating satellites over any givengeographic area for which a radio route is being established, such asthe area CA in FIG. 6. Thus, the likelihood of quickly establishing arelatively long-lasting radio route is increased by deploying at leastsome, and preferably about one-half, of the satellites rotating in theopposite direction from the others. In addition, not only are twoantennas on respective satellites in alignment longer, but as soon asthey rotate out of view of each other, two other antennas of thesatellites may align, thus enabling rapid refreshing of the radio linkbetween the satellites. In the example illustrated in FIG. 8B, antenna12 ₁ in satellite S₁ and antenna 12 ₅ in satellite S₂ will align next.

Like the example used to illustrate the increased efficacy of usingrotating satellites discussed just above, this is also an idealizeddescription of how counter-rotating satellites can create longer lastingradio links between them. In addition, to the assumptions underlying theabove description, there may not be at any given time twocounter-rotating satellites over an area where a radio route is desiredbetween two ground stations. Nevertheless, taken together, theseexamples illustrate the point that rotating satellites, and particularlycounter-rotating satellites, will provide a sufficient probability ofestablishing a relatively high gain radio link between the random orbitsatellites to enable reliable data communications between two groundstations via one or more satellites. And because the antennas point in aplurality of directions (preferably over the entire spherical spacesurrounding the satellite), the opportunity for establishing a radiolink between two spinning satellites will in most instances be enhancedby using rotating satellites.

2. Satellites with Different Angular Velocities

A variation of the embodiment described just above employs satellitesthat rotate at different angular velocities. This variation is depictedschematically in FIG. 8C, in which the satellite S₁ rotates at anangular velocity ω₁ and S₂ rotates at a different angular velocity ω₂.The advantage of this system is that the antennas on thecounter-rotating satellites may be out of phase in the sense thatantenna on one satellite may be pointing directly to a space betweenantennas on a second satellite, as depicted in FIG. 8C. If thesatellites are rotating at the same angular velocity, this situation canpersist for an extended period of time, thus weakening a radio linkbetween the satellites, or perhaps preventing the establishment of alink altogether. Rotating the satellites at different angular velocitieswill increase the likelihood that at some angular position antennas onboth satellites will face each other (be in phase), thus enabling theestablishment of a useful radio link between them. For example, in thecase illustrated in FIG. 8C, the antennas on the satellites are exactly180° out of phase, in that the antenna 12 ₂ on satellite S₁ is pointingdirectly at the space between the antennas 12 ₄ and 12 ₅ on satelliteS₂. If ω₁=1.33×ω₂, the antenna 12 ₅ on satellite S₂ and the antenna 12 ₅on satellite S₂ will line up as the satellites rotate.

It is anticipated that certain installations of the system will utilizenumerous satellite to satellite links, while at the same time being ableto tolerate some delays transmitting calls between ground stations. Thistype of installation can benefit from using satellites that rotate atslightly different angular velocities. In other words, the system wouldbe designed to increase the probability that a satellite transmitting aradio signal would rotate at a different angular velocity than asatellite receiving the signal. The data communications might be delayedwhile the radio route is intermittently disrupted and refreshed asdifferent antennas on the two satellites disalign and realign. However,this can be compensated for by buffering the data communications andsending them each interval when the radio link is present.

In an exemplary approach, the cohort of satellites could be divided intofive groups with different angular velocities in accordance with thefollowing table.

TABLE 4 Very slow spinner: 0.68 revolutions per second Slow spinner:0.84 revolutions per second Average spinner:  1.0 revolution per secondFast spinner: 1.16 revolutions per second Very fast spinner: 1.32revolutions per second

The discussion immediately above explains how this can tend to increasethe probability of establishing beam matches between the antennas onrespective satellites. That is, the above discussion demonstrated oneinstance of how a satellite rotating at an angular velocity 1.33 timesthe angular velocity of another can facilitate a beam match. The sameprinciple applies for other multiples of angular velocity.

By the same token, this system implementation will also make more beammatches possible in a given time period because the antennas on onesatellite will have more opportunities to line up sufficiently withantennas on another satellite to form beam matches if the satellites arecounter-rotating at different angular velocities. There may be no beammatches between two satellites at a given time, or for a certaininterval, as they rotate. However, as they continue to rotate atdifferent angular velocities, antennas on the satellites will likelyform beam matches because antennas on the respective satellites will belikely to line up at some point. This may take plural revolutions of thesatellites, but rotation at different angular velocities greatlyincreases the probability that many more matches will be created as thesatellites continue to rotate. It will thus be appreciated from thecomplex interrelationship of the antennas on different satellites as thesatellites move in their orbits and rotate about their axes thatproviding plural cohorts of satellites rotating at respective differentangular velocities will increase the probably of creating more beammatches between pairs of the satellites during any given time interval.Any resulting delays while beam matches are created may be tolerable ifthe alternative is an inability of a particular ground station to sendand receive data transmissions at all.

3. Other Considerations

It is known that the angular velocity of a body rotating in earth orbit,especially at lower altitudes, is subject to decay from a number offactors. For example, even though the earth's atmosphere is extremelythin at low- and medium-earth orbital altitudes, the region in whichsatellites used in the present system will preferably occupy, orbitingobjects nevertheless still experience aerodynamic drag. Forces generatedby the passage through the earth's magnetic field of ferromagneticmaterials in the object can also affect the angular velocity of arotating body such as a satellite. The tendency of the rotatingsatellites to undergo a reduction in angular velocity over time can becompensated for in a variety of ways. One is to use retro rockets oractive mechanical devices known in the prior art. However, since one ofthe objects of the invention is to minimize the cost of building,deploying, and maintaining the satellites used in the radio systemsdescribed herein, it is preferred to use passive means for compensatingfor external forces on the satellites or for creating forces to controlsatellite movements.

One such means uses solar panels with solar cells only on one side toutilize the momentum of photons striking the panels to create a torqueabout the rotational axis of the satellite. For example, referring toFIGS. 3 and 4, for a satellite that is deployed to rotatecounterclockwise about the z-axis (as viewed in the negative-zdirection), each solar panel 14 a would have solar cells only on oneside, namely the side facing the viewer for the solar panel 14 a to theright in FIG. 4 and the side facing away from the viewer for the othersolar panel 14 a to the left in FIG. 4. The remaining solar panels wouldstill have solar cells on both sides. Although larger solar panels willincrease aerodynamic drag on the satellite, it is believed that it willbe possible through judicious design to provide solar panels of a size,configuration, and orientation that will generate a net torque on thesatellite that overcomes the tendency of the angular velocity to decay.

It is likewise believed possible to selectively distribute the mass ofthe satellite components to cause it to rotate about a particular axis.Since it is anticipated that the battery will form a large proportion ofthe satellite mass, it will preferably be located at the center of massof the satellite and have a mass distribution that is symmetric aboutthe axis of rotation. In addition, the effects of the earth's magneticfield on the satellites can be minimized by using non-ferromagneticmaterials such as aluminum wherever possible. These features, inaddition to the use of the solar panels to provide a moment about therotational axis, will suffice to at least reduce the rate of decay ofthe satellites' angular velocity.

As mentioned above, some or all of the above passive means forcontrolling satellite movement can be employed in the tumbling satelliteembodiment. That is, in one variation one or more solar panels can havesolar cells on only one side to impart an unbalanced moment on thesatellite to cause it to continue to tumble. Another variation couldlocate ferromagnetic materials in selected locations on the satellitethat will produce forces that vary in magnitude and direction as thesatellite traverses the earth's magnetic field.

Since satellites originally deployed to rotate will likely remain inorbit even if their initial angular velocity decays over time, they willstill be available as nodes in a radio route between ground stations.Since satellites in accordance with the present system are inexpensiveto construct, launch, and deploy, additional rotating satellites can belaunched to replace any whose angular velocity has decayed. This willnot only increase the number of satellites available for route creation,but to the extent that any of the older satellites remain spinning, theeffect will be to automatically take advantage of the improvedperformance made capable by using satellites rotating at differentangular velocities.

V. Other Modifications and Variations

It will be appreciated that numerous variations and modifications of thestructures and methods described heretofore are possible within thescope of the present invention. The above exemplary embodiments useaddition of the figures of merit of two potential radio links to selecta preferred radio route. However, the invention encompasses other waysof determining a preferred route, since using the sums of the figures ofmerit for two different potential radio routes would favor a multiplesatellite route over a single satellite route. Thus, although additionof the figures of merit in a single satellite route will typicallyresult in an optimum or preferred route, more complex and sophisticatedalgorithms may be necessary to implement this aspect of the inventionwhen choosing between potential single- and multiple-satellite routes orbetween two potential multiple-satellite routes. One possible approachin those situations would be to select a particular route when otherpotential routes would include a link judged to be inferior for one ormore reasons, some examples of which are discussed above (inadequatesignal strength and/or excessive error rate between various nodes in apotential multiple satellite route, low remaining satellite batterylife, excessive link loading, or eliminating potential links withfigures of merit below a predetermined threshold).

Those skilled in the art will recognize that “figure of merit” asdiscussed herein is simply one way of articulating the important conceptof choosing a radio route deemed to be optimum for data communicationsbetween two ground stations. The parameters used in determining a figureof merit for a particular potential link are not limited to thosespecifically pointed out in this description. One example would takeinto account that the satellites are moving relative to each other, sothat the quality of potential links between satellites or between asatellite and a ground station will change over time. Thus, one of thefactors in selecting a link could be the derivative of link quality(figure of merit) with respect to time, since a positive value wouldindicate that the link quality would increase and thus be more stable,while a negative value would indicate the opposite.

It will be appreciated by those skilled in the art that the radio systemdescribed herein is not limited to implementation using satellites assystem nodes. For example, nodes similar in construction to thesatellites described above can be suspended from balloons that areallowed to drift freely in the stratosphere (or at lower altitudes). Theballoon-mounted nodes would include antennas corresponding to thesatellite antennas described above arranged in the nodes fortransmitting and receiving signals in plural directions. Anothervariation could mount such nodes on unmanned aerial vehicles (“drones”)deployed randomly over a particular area. It is believed that such asystem would enable communications directly from hand-held devices morereadily than a satellite-based system because the drones would be closerto the ground stations (hand-held devices) than in a satellite nodesystem.

VI. Summary and Conclusion

Those skilled in the art will readily recognize that only selectedpreferred embodiments of the invention have been depicted and described,and it will be understood that various changes and modifications can bemade other than those specifically mentioned above without departingfrom the spirit and scope of the invention, which is defined solely bythe claims that follow.

What is claimed is:
 1. A radio communications system comprising multiplesatellites orbiting the earth for providing a radio route for datacommunications between transceivers at two ground stations, eachsatellite and ground station comprising a node of the system, whereineach of a plurality of the satellites includes: a plurality of satelliteantennas for receiving an initial radio signal from at least one groundstation and for transmitting routing signals; antenna pairing circuitryfor storing address information identifying a ground station from whichthe satellite received an initial radio signal and the identity of thesatellite antenna on which the satellite received the initial radiosignal; and route creation circuitry for transmitting routing signalsfrom a plurality of the satellite antennas, wherein the routing signalscomprise (i) linking information including an address of the groundstation that sent the initial radio signal, and (ii) a quality of thereceived initial radio signal indicating a suitability of the satelliteas a node in a radio route to the ground station identified by thestored address.
 2. The radio communications system in claim 1, whereinthe satellite antennas are directional antennas.
 3. The radiocommunications system in claim 2, wherein the satellite antennas arearranged to transmit and receive radio signals in multiple directionsaround substantially the entire spherical space each of the satellites.4. The radio communications system in claim 2, wherein the satelliteantennas are arranged to transmit and receive radio signals in multipledirections around less than the entire spherical space surrounding eachof the satellites.
 5. The radio communications system in claim 1,wherein the satellite nodes are designated as a first type and theground station nodes are designated as a second type, and nodes of thesame type do not communicate with each other.
 6. The radiocommunications system in claim 1, wherein the routing signals comprisepackets of digital data, each packet including: a header containing thelinking information and the quality of the received initial radiosignal; and a payload including a sample data stream used by anothernode receiving a routing signal to determine the quality of the routingsignal received from the satellite.
 7. The radio communications systemin claim 6, wherein the quality of the received routing signal isexpressed as a quantitative figure of merit based at least in part on anerror rate of the sample data stream.
 8. The radio communications systemin claim 1, wherein each of the plurality of the satellites furtherincludes a plurality of solar panels, at least one solar panel beingoriented to generate electricity regardless of satellite orientationwhen the satellite is exposed to solar radiation during its orbit. 9.The radio communications system in claim 8, wherein each of theplurality of the satellites further includes a battery module forproviding electrical power to the satellite antennas, antenna pairingcircuitry, and route creation circuitry, the battery module beingcharged by the at least one solar panel when the satellite is exposed tosolar radiation during its orbit.
 10. The radio communications system inclaim 8, wherein the solar panels are constructed to cause thesatellites to rotate in orbit.
 11. The radio communications system inclaim 1, wherein the satellites orbit the earth in orbital paths locatedrandomly relative to each other without attitude control.
 12. The radiocommunications system in claim 11, wherein the satellite antennas aredirectional antennas.
 13. The radio communications system in claim 12,wherein the satellite antennas are arranged to transmit and receiveradio signals in multiple directions around substantially the entirespherical space surrounding each of the satellites.
 14. The radiocommunications system in claim 12, wherein the satellite antennas arearranged to transmit and receive radio signals in multiple directionsaround less than the entire spherical space surrounding each of thesatellites.
 15. The radio communications system in claim 1, wherein thesatellites orbit the earth in uncontrolled orbits.
 16. A method forcreating a radio communication route for data communications from areceiving ground station to a sending ground station, wherein the groundstations include a plurality of ground station directional antennas fortransmitting and receiving radio signals, the method comprising: (a)providing multiple satellites orbiting the earth, wherein each of aplurality of the satellites includes a plurality of satellitedirectional antennas for transmitting and receiving radio signals; (b)receiving at a satellite antenna of at least one satellite an initialinformation signal transmitted from an antenna at a sending groundstation; (c) storing at any satellite receiving the initial informationsignal at least (i) address information identifying the ground stationfrom which the initial information signal was received, and (ii) theidentity of the satellite antenna on which the initial informationsignal was received; (d) transmitting linking information signals from aplurality of the antennas of at least one satellite receiving theinitial information signal, wherein the linking information signalscomprise (i) linking information including an address of the groundstation that sent the initial information signal, and (ii) a quality ofthe received initial information signal indicating a suitability of thesatellite as a node in a radio route to the ground station identified bythe stored address; (e) storing at a receiving ground station receivingat least one linking information signal (i) the receiving ground stationantenna on which the linking information signal was received, and (ii) aquality of the initial information signal received at the satellitetransmitting the linking information signal; and (f) determining aquality of a radio route for data communications from the receivingground station to the sending ground station via a particular satellitebased on (i) a quality of the received linking information signalindicating a suitability of the particular satellite as a node in aradio route from the receiving ground station, and (ii) the quality ofthe initial information signal.
 17. The method in claim 16, wherein thesatellites are designated as a first type of node and the groundstations are designated as a second type of node, and nodes of the sametype do not communicate with each other.
 18. The method in claim 17further including sending a data transmission from the receiving groundstation to the sending ground station, wherein the first type of nodeonly transmits radio signals in a first mode and only receives radiosignals in a second mode that substantially eliminates interference withtransmissions in the first mode, and the second type of node onlyreceives radio signals in the first mode and only transmits radiosignals in the second mode.
 19. The method in claim 16, wherein: theinitial information signal comprises packets of digital data including aheader containing at least the sending ground station addressinformation and a payload including a sample data stream used by thesatellite to determine the quality of the received initial informationsignal; and the linking information signal comprises packets of digitaldata including a header containing at least the linking information andthe quality of the received initial information signal and a payloadincluding a sample data stream used by the receiving ground station todetermine the quality of the received linking information signal. 20.The method in claim 19, wherein the qualities of the initial informationsignal received by the satellite and the linking information signalreceived by the receiving ground station are expressed as quantitativefigures of merit based at least in part on an error rate of therespective sample data streams.
 21. The method in claim 20 furtherincluding communicating a data transmission comprising packets ofdigital data from an origin comprising a receiving ground station to adestination comprising a sending ground station, each data transmissionpacket including a header including the address information of thedestination and a payload including a data stream representing thecontent of the transmission, wherein: the origin transmits the packet ofdigital data to the particular satellite using the receiving groundstation antenna on which the linking information signal was received;and the particular satellite transmits the packet of digital datatransmission to the destination using the antenna of the particularsatellite on which the initial information signal was received.
 22. Themethod in claim 21, wherein the data transmission includes a pluralityof packets and the header includes sequence information indicating theoriginal order of the packets comprising the content of thetransmission, the radio route from the origin to the destination usesdifferent satellites during the data transmission, and the destinationuses the sequence information to place the packets in the originalorder.
 23. The method in claim 16, wherein the satellite antennas arearranged to transmit and receive radio signals in multiple directionsaround substantially the entire spherical space surrounding thesatellites and the ground station antennas are arranged to transmit andreceive radio signals in multiple directions around substantially theentire semi-spherical space above the surface of the earth surroundingthe ground stations.
 24. The method in claim 16 further includingcommunicating a data transmission comprising packets of digital datafrom an origin comprising the receiving ground station to a destinationcomprising the sending ground station, each data transmission packetincluding a header including the address information of the destinationand a payload including a data stream representing the content of thetransmission, wherein: the origin transmits the packet of digital datato the particular satellite using the receiving ground station antennaon which the linking information signal was received; and the particularsatellite transmits the packet of digital data transmission to thedestination using the antenna of the particular satellite on which theinitial information signal was received.
 25. The method in claim 16,wherein the satellite antennas are arranged to transmit and receiveradio signals in multiple directions around less than the entirespherical space surrounding each of the satellites.
 26. The method inclaim 16, wherein the determining step is performed by the receivingground station without a controlling computer communicating with thesatellites or other ground stations.
 27. The method in claim 16, furthercomprising deploying the satellites with a rotational velocity about anaxis of rotation.
 28. The method in claim 16, wherein the satellitesorbit the earth in orbital paths located randomly relative to each otherwithout attitude control.
 29. The method in claim 16, wherein thesatellites orbit the earth in uncontrolled orbits.
 30. A radiocommunication route for data communication from an originating groundstation to a destination ground station, the route comprising at leastone of multiple satellites orbiting the earth that communicate with theground stations, each ground station including a plurality ofdirectional antennas for receiving radio signals from multipledirections and transmitting radio signals in multiple directions,wherein each of the multiple satellites includes: a plurality ofdirectional antennas for receiving radio signals from multipledirections and transmitting radio signals in multiple directions;antenna pairing circuitry for storing address information identifying adestination ground station from which an initial information signal wastransmitted and the identity of the antenna on which the satellitereceived the initial information signal; and route creation circuitryfor transmitting linking information signals from a plurality of thesatellite antennas, the linking information signals comprising linkinginformation including an address of the destination ground station thatsent the initial information signal, whereby data transmissions receivedat the originating ground station and designating the destination groundstation are transmitted by the originating ground station using a groundstation antenna on which a linking information signal was received andthe satellite transmits the data transmission using the satelliteantenna the identity of which is stored in the satellite.
 31. The radiocommunication route in claim 30, further including plural satellites,wherein: the antenna pairing circuitry in a first satellite of saidmultiple satellites stores address information identifying a destinationground station from which it received an initial information signal andfirst satellite antenna information identifying the antenna of the firstsatellite on which the initial information signal was received; theroute creation circuitry in the first satellite transmits intermediatelinking information signals from a plurality of the antennas of thefirst satellite; the antenna pairing circuitry in an n^(th) satellitestores the identity of the antenna of the n^(th) satellite on which theintermediate linking information signal was received; and the routecreation circuitry in the n^(th) satellite transmits n^(th) linkinginformation signals from a plurality of the antennas of the n^(th)satellite, whereby data transmissions received at the originating groundstation and designating a particular destination ground station aretransmitted by the originating ground station using the antenna on whichan n^(th) linking information was received, the n^(th) satellitetransmits the data transmission data using the antenna the identity ofwhich is stored in the n^(th) satellite, and the first satellitetransmits the data transmission data using the antenna the identity ofwhich is stored in the first satellite.
 32. The radio communicationroute in claim 30, wherein: a first predetermined number of the multiplesatellites are designated as a first type of node and the groundstations are designated as a second type of node, and nodes of the sametype do not communicate with each other; and at least one satellite isdesignated as the second type of node.
 33. The radio communication routein claim 30, comprising a first intermediate radio route between thedestination ground station and an intermediate ground station via afirst satellite and a second intermediate radio route between theintermediate ground station and the originating ground station via asecond satellite.
 34. The radio communication route in claim 30,wherein: the satellites rotate about a rotational axis; and each of themultiple satellites further includes a plurality of solar panelsconstructed to impart a moment on the satellite about the rotationalaxis.
 35. The radio communication route in claim 30, wherein thesatellite antennas are arranged to transmit and receive radio signals inmultiple directions around substantially the entire spherical spacesurrounding each of the multiple satellites.
 36. The radio communicationroute in claim 30, wherein the satellite antennas are arranged totransmit and receive radio signals in multiple directions around lessthan the entire spherical space surrounding each of the multiplesatellites.
 37. The radio communication route in claim 30, wherein eachof the plural satellites orbit the earth in orbital paths locatedrandomly relative to each other without attitude control.
 38. The radiocommunication route in claim 37, wherein the linking informationincludes a quality of the received linking information signal indicatingthe suitability of the satellite as a node in the radio communicationroute.
 39. The radio communication route in claim 38, wherein theoriginating ground station receives linking information signals frommore than one of the multiple satellites and selects one of the multiplesatellites as the node for data transmission based on the qualities ofthe linking information signals.
 40. The radio communication route inclaim 30, wherein the plural satellites orbit the earth in uncontrolledorbits.
 41. A method of transmitting data communications from theoriginating ground station to the destination ground station using theradio communication route of claim 30, the method comprising: providingto the originating ground node a data transmission designating theaddress of the destination station in encrypted form and a payloadincluding a data stream representing the content of the transmission;and only destination ground stations in a predetermined geographic areainclude decryption keys enabling access to the data stream.
 42. A methodof transmitting data communications from the originating ground stationto the destination ground station using the radio communication route ofclaim 34, the method comprising: providing a data transmissioncomprising packets of digital data to the originating ground node, eachdata transmission packet including a header designating the address ofthe destination station in encrypted form and a payload including a datastream representing the content of the transmission; and onlydestination ground stations in a predetermined geographic area includedecryption keys enabling access to the data stream.